Real Estate Facilities (Narrative) (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($) ft² item	Jun. 30, 2019 USD ($)
Schedule Of Real Estate Facilities [Line Items]
Write-off of cancelled projects	$ 3,200	$ 3,226
Increase (decrease) in accrued unpaid construction costs		(4,000)	$ (16,600)
Increase (decrease) in accrued capital expenditures to maintain real estate facilities		$ (4,300)	$ 1,500
Acquisition Of Self-Storage Facilities Other Investments [Member]
Schedule Of Real Estate Facilities [Line Items]
Number of operating self-storage facilities | item		15
Net rentable square feet | ft²		1,167,000
Total cost of acquisition		$ 253,300
Allocated to intangible assets	$ 10,000	10,000
Newly Developed and Expansion Projects [Member] | Completed Developed and Expansion Project [Member]
Schedule Of Real Estate Facilities [Line Items]
Aggregate costs to develop and expand		$ 70,000
Addtional net rentable square feet | ft²		500,000